The objective of the proposed research is to determine whether microbial calcification can provide a model system for vertebrate calcification. A crude phospholipid extract of Bacterionema matruchotii has been shown to initiate hydroxyapatite formation when exposed to metastable calcium phosphate solutions. There appears to be a similar factor in dental calculus matrix, marmoset femur matrix, and elephant tusk matrix which is responsible for apatite nucleation. In B. matruchotii the nucleating entity is composed of a basic protein-acidic phospholipid complex. A non-calcifying acridine orange induced mutant of B. matruchotii has been isolated. By purifying and comparing the phospholipid extracts of the parent organism and its mutant, this research seeks to elucidate the mechanism of intracellular calcium phosphate deposition. If the AO mutant extract also supports apatite formation, studies will be initiated to determine possible alterations in cellular metabolism responsible for loss of calcifiability.